Drive arrangement

ABSTRACT

A drive arrangement for converting rotary motion to linear motion in which a rotating member co-operates with a co-operating member on a follower member, the follower moving along a line transverse to the axis of rotation of the rotating member and the co-operating member moving transversely both to the line and the axis of rotation.

United States Patent 1 Grantham 1 Feb. 26, 1974 1 DRIVE ARRANGEMENT [75]Inventor: Max Edward Grantham, Plympton,

Plymouth Devon, England [73] Assignee: Tecalemit (Engineering) Limited,Devon, England 22 Filed: Oct. 18, 1972 211 Appl. No.: 298,610

[30] Foreign Application Priority Data Oct. 18, 1971 Great Britain48445/71 [52] US. Cl 74/50, 92/129, 417/471 [51] Int. Cl F1611 21/18[58] Field of Search... 74/50; 92/129; 417/470, 471

[56] References Cited UNITED STATES PATENTS 853,707 5/1907 Margadant74/50 2,957,420 10/1960 Reynolds et a1. 92/129 1,904,799 4/1933 Palmer417/471 3,545,896 12/1970 Zahradnik 417/471 Primary Examiner-Benjamin W.Wyche Assistant Examiner-Wesley S. Ratliff, Jr.

[ 5 7 1 ABSTRACT A drive arrangement for converting rotary motion tolinear motion in which a rotating member co-operates with a co-operatingmember on a follower member, the follower moving along a line transverseto the axis of rotation of the rotating member and the cooperatingmember moving transversely both to the line and the axis of rotation.

2 Claims, 6 Drawing Figures SHEET 3 BF 4 FIGS.

DRIVE ARRANGEMENT BACKGROUND OF THE INVENTION The invention relates todrive arrangements for converting rotary motion to linear motion. Drivearrangements are known having a rotatable member rotatable about anaxis, said rotatable member including a first co-operating member spacedfrom said axis, a follower member mounted for movement along a linetransverse to said axis, said follower member including a secondco-operating member, the first and second cooperating membersco-operating with one another so that as the rotatable member rotatesand the first cooperating member describes a circular path about saidaxis the second co-operating member moves the follower member along saidline.

An example of this kind of drive arrangement is a pin and slot drivearrangement, the pin being carried by the rotatable member and formingsaid first co-operating member and the slot comprising the secondcooperating member being carried by a member restrained to movelinearly. In a second example the slot may be open on one side and thusbe provided by a cam surface on the follower member so that the pin canonly move the follower member in one direction along said line in whichcase the follower member might be moved in the other direction by aresilient member. In a third example, it may be arranged that when thefollower member begins to move in the other direction the pin becomesdisengaged from the cam surface to allow the resilient member alone tocontrol the movement of the follower member in said other direction.

In all of these arrangements there are considerable friction lossesbetween the pin and the slot or cam surface. The friction losses aresmall when the pin is moving approximately transversely to the slot orcam surface, but when at another point on its path it is movingapproximately parallel thereto considerable friction losses result.Also, in certain uses of such a drive arrangement such as when the pinis rotated about the axis slowly, it has been found that when the pin ismoving approximately parallel to the slot or cam surface that stick-slipoccurs. This is the phenomena in which the pin will not move across theslot or cam surface until sufficient torque has been built up when itsuddenly moves quickly for a short distance until it sticks relative tothe surface once again. Thus, the pin moves across the surface in aseries of jerks. This causes irregularities in the drive and henceexcessive wear and also requires that, for rotating the rotatablemember, a motor of higher power than would otherwise be necessary isrequired.

SUMMARY OF THE INVENTION It is an object of the present invention toprovide a drive arrangement in which friction losses are considerablyreduced.

It is a further object of the present invention to provide a drivearrangement in which stick-slip does not occur.

According to the present invention there is provided a drive arrangementfor converting rotary motion to linear motion comprising a rotatablemember rotatable about an axis and having a first co-operating memberspaced from said axis, a follower member mounted for movement along aline transverse to said axis, said follower member including a secondco-operating memher movable generally transversely of said line and ofsaid axis with said first co-operating member, the first and secondco-operating members co-operating with one another so that, as therotatable member rotates and the first co-operating member describes acircular path about said axis, the second co-operating member moves thefollower member along said line.

Accordingly, in the drive arrangement according to the present inventionno relative movement between the two co-operating members takes placeexcept a rolling motion so that frictional losses between the twoco-operating members are reduced. Preferably the follower member and thesecond co-operating member are fixed relative to one another. This maybe arranged by providing the follower member in the general form of ashaft extending along said line and rotatable about its axis to providethe movement of the second cooperating member attached thereto generallytransversely to said line and said axis. The shaft may be mounted inbearings.

In the case where the first co-operating member is provided by a pin andthe second co-operating member is in the form of a cam surface, the pinbearing against the cam surface to move the follower member in onedirection along said line, and biassing means being provided to move thefollower member in the opposite direction, the biassing means may be inthe form of a coil spring. If the follower member is in the form of ashaft then it may be coaxially mounted with the coil spring, the coilspring bearing on the shoulder of the shaft so that movement of the camsurface generally transversely of said line and the axis may cause thecoil spring to wind up or unwind.

The drive arrangement is suitable for application to a piston pump andthe invention therefore also provides a pump including a drivearrangement as aforesaid in which the follower member is connected tothe piston of the pump. In this case, the follower member in the form ofthe piston may easily rotate about its axis since there will be littlefriction between the piston and the cylinder walls.

Piston pumps having drive arrangements incorporating preferredembodiments of the invention will now be described by way of exampleonly and with reference to the accompanying drawings in which:

FIG. 1 is a general view of a pump;

FIG. 2 is a cross-section of the pump of FIG. 1;

FIG. 3 is a diagram of the principle of operation of the drive system ofthe pump;

FIG. 4 is a perspective view of the pin;

FIG. 5 is a front view, partly in section, of another pump; and

FIG. 6 is a cross-section of the pump body of the pump of FIG. 5.

Referring to FIGS. 1 and 2, the pump 10 shown in FIG. 1 is designed foruse with a central lubrication system in which the pump forces lubricantthrough a network of pipes to various parts of the machine, such as aprinting or a textile machine, to which it is attached. The pump 10 ismounted on a lid 11 of a lubricant reservoir (not shown), the pump body12 extending downwardly from the lid 11 into the lubricant. A seal 13 isprovided for sealing the lid 11 to the reservoir. The pump body 12includes a cylinder barrel 14 to the bottom of which is attached aremovable filter housing and element 16. The lower end of the cylinderbarrel 14 extends into the lubricant so that the lubricant can flowthrough the housing 16 into the cylinder barrel 14. The lower end of thecylinder barrel above the filter housing 16 is closed by one-way inletvalve 17 which allows lubricant to enter but not to leave the cylinderbarrel 14. A fluid outlet 18 is also provided on one side of the lowerend of the cylinder barrel 14. Fluid outlet 18 includes a one-way valvewhich allows lubricant to flow from but not into the cylinder barrel 14.The fluid outlet 18 is connected by a flexible tube to an outlet nipple19 situated in the lid 11 of the pump. The cylinder barrel 14 provides apumping chamber 21 in which is situated a piston 22. The upper half ofthe pump body 12 above the cylinder barrel 14 is cut away so as to havea semi-circular cross-section, this part of the pump body 12 providing asupport bracket for the cylinder barrel. The upper end of the pump body12 is rigidly connected to the lid 11, the lid 11 being situated betweena shoulder 23 on the pump body 12 and a lock nut 24 above the lid. Locknut 24 is threaded on to the threaded upper end of the pump body 12.

A piston rod 26 extends upwardly from the piston 22 and incorporates asecond piston 27 in the cylinder barrel 14 which acts as a back-uppiston. The two pistons 22, 27 act as bearings for maintaining thepiston rod 26 in an upright position. The upper end of the piston rod 26engages the lower end of a follower member in the form of a tubularsleeve 28 which passes upwardly through the lid 11 and the lock nut 24with which it slidingly engages. The upper end of the sleeve 28 carriesa hand knob 29. As will be seen from FIG. 2 of the drawings the upperend of the piston rod 26 is surrounded by the sleeve 28. The sleeve 28is internally threaded at 31 and threadingly engages the upper end ofthe piston rod 26. The top end of the piston rod carries a screw slot 32which allows the piston rod to be rotated by a screwdriver insertedthrough a passageway passing through the hand knob 29. Rotation of thepiston rod by the screwdriver moves the piston rod 26 upwardly ordownwardly relative to the sleeve 28. The screw slot 32 is normallyprotected by a grub screw 33.

Rigidly attached to the bottom end of the sleeve 28 and surrounding thesleeve is an annular drive plate 34. The drive plate 34 is clamped tothe sleeve 28 and the swaged endof the sleeve 28. The upper surface ofthe drive plate 34 carries a spring seat 36. A coil spring 37 extendsbetween this spring seat 36 through the lid 11 to abut the underside ofthe lock nut 24. The coil spring 37 thereby biasses the piston assembly(which comprises pistons 22, 27, piston rod 26, sleeve 28, drive plate34, hand knob 29) downwardly until the piston 22 abuts the upper surfaceof the one-way inlet valve 17.

It will be appreciated that all of the piston assembly is mounted so asto be freely rotatable about the axis of the piston rod 26 except for aslight restoring force provided by the coil spring 37. The coil spring37 is chosen so as to provide a very low restoring force, that is, thespring can readily be wound up by rotation of the drive plate 34.

Referring to FIGS. 1, 2 and 3, drive means are provided to lift thepiston against the bias of the coil spring 37. The drive means comprisesan electric motor 38 mounted on the top of the lid 11, a drive outputshaft 39 of the motor 38 passing downwardly through the lid 11 insuitable bearings and carrying at its lower end a gear wheel 41. Thegear wheel 41 meshes with a further gear wheel 42 which drives asubstantially horizontal shaft 43. Shaft 43 extends towards the pumpbody 12 and is suitably joumalled in bearings 44 in a bracket 46depending from the lid 11. At its end closest the pump body 12, thedrive shaft 43 carries a transverse block 47 keyed thereto so as to berotatable with the drive shaft 43. The transverse block 47 carries a pin48 spaced from the axis 45 of rotation of the drive shaft 43, the pinprojecting towards the piston rod 26. As shown in FIG. 2 the pistonassembly is in its lowermost position and the pin rotated about the axis45 of the drive shaft 43 so as to be in its lowermost position, the pin48 is situated and extends just below the lowermost surface of the driveplate 34. As can be seen from FIG. 1 it will be noted that the axis 45of the drive shaft 43 is offset from the axis of the piston rod 26, thedirection of rotation of the drive shaft 43 being such that the pin 48is moved towards the axis of the piston rod 26 during the lower half ofits rotary motion about the axis of the drive shaft 43 and moves awayfrom the axis of the piston rod 26 during the upper part of this motion.

Reffering to FIGS. 1 2 and 4, the shape of the pin 48 is shown moreclearly in FIG. 4. The pin comprises a rod of circular cross-sectionrigidly mounted in the transverse block 47 the end portion 49 of whichis of slightly larger diameter than the adjacent inwardly disposedportion 51. The portion 49 is relieved by a flat surface 52 extendingfrom a diameter 49a on the outer end face of portion 49 to a chord 49bon inner end face of portion 49, the chord 49b being parallel todiameter 49a. Flat surface 52 subtends an angle of 45 with thelongitudinal axis of pin 48. The pin 48 is mounted in the transverseblock 47 so that the plane of the flat surface 52 is substantiallyvertical when the pin 48 is in its uppermost or lowermost position asthe drive shaft 43 rotates, the flat surface 52 being provided on theside of the pin facing away from the direction of its rotation.

The mode of operation is as follows. The oil level in the reservoir isabove the level of the filter housing 16 and thus when the piston 22 israised oil is drawn into the pumping chamber 21 through the one-wayinlet valve 17. When the piston then moves downwardly the oil in thepumping chamber 21 is forced out of the outlet 18 to the outlet nipple19 and thence to the lubricating system. Upward movement of the piston22 is caused by the drive system and downward movement of the piston 22is caused by the spring 37. It will be appreciated that since oil isbeing pumped the two pistons 22 and 27 are continuously lubricated andthat very little friction loss can occur between the pistons and thecylinder barrel.

The operation of the drive system will now be described in more detail.Referring to FIGS. 1, 2 and 3, the motor 38 is continuously driven androtates the drive shaft 43 via the output shaft 39 and the gears 41, 42.The motor 43 is arranged to rotate very slowly since for mostapplications it is necessary only to pump oil infrequently since eachbearing only requires a small quantity of oil over a period of time.Rotation of the drive shaft 43 causes rotation of the transverse block47 and hence causes movement of the pin 48 around a circular path. Thecircular path 54 of the pin 48 is shown in FIG. 3 which illustratesdiagrammatically the method of engagement of the pin 48 with the driveplate 34. Drive plate 34 accordingly acts as a cam member. ConsideringFIG. 3, it will be seen that the lowermost position of the drive plate34 is illustrated at A, that is when the piston 22 is bearing on theinlet valve 17. The pin 48 is rotated by the drive shaft 43 so as topass under the drive plate 34 in its lowermost position, the pin 48first contacting the underside of the drive plate 34 at the point B. Asthe pin 48 continues to rotate about the axis 45 it lifts the driveplate 34, which further compresses the coil spring 37. At the same timeit will be appreciated that the pin 48 moves across the plane of thedrive plate 34. Hitherto, this has caused stick-slip problems as notedabove which are particularly accentuated since the movement is very slowgiving the pin every opportunity to stick. It will be appreciated,however, that as the pin 48 moves across the plate of the drive plate 34in the present embodiment, the drive plate 34 can move with the pin 48since it is substantially freely mounted so as to be rotatable about theaxis of the piston rod 26. Thus, as the pin moves from the position inwhich it contacts the plate 34 at B up to a position C, the drive plate34 rotates about the axis of the piston rod so that substantially the Isame point of the drive plate 34 remains in contact with the pin 48.There is, however, a rolling motion of the pin 48 across the surface ofthe drive plate 34 so that the pin 48 will be displaced slightly acrossthe drive plate 34. During this rotation of the drive plate 34 by thepin, the coil spring 37 is slightly wound or unwound as the case may be.During movement of the pin from position C to position D, the driveplate will rotate back substantially to its original position unwindingor winding the coil spring so as to restore it to substantially itsoriginal position.

It will be appreciated that whilst previous arrangements have beendesigned to reduce the friction between the pin 48 and the drive plate34, for example, by providing the pin 48 in the form of a roller andallowing the roller to roll across the surface of the drive plate 34,the present arrangement provides a fundamentally different solution,that is, mounting the drive plate 34 so as to be movable in its ownplane with the pin 48 and thereby eliminating the friction lossesbetween these two parts.

As has been stated above, the movement of the pin about its circularpath 54 is very slow and if the pin were allowed to remain in contactwith the drive plate 34 during the pumping stroke, there is a likelihoodthat no pressure would be developed during this pumping stroke sincemovement of the piston 22 during the pumping stroke would be so slowthat a lubricant pressure would not be built up. Thus, at the point Dthe pin moves away from the drive plate 34. This allows the drive plate34 to move from its uppermost position E to which it has been raised bythe pin 48 just before reaching position D, back to position A under theinfluence of the coil spring 37 which has been further compressed. Ifthe end portion 49 of pin 48 had a simple cylindrical shape, then driveplate 34 would be in contact with the pin 48 for a short distance afterthe position D is reached i.e. at the beginning of the downward strokeof drive plate 34. Accordingly, the pin 48 would tend to slow down thepiston assembly at the start of the downward stroke and pin 48 would besubject to a force tending to move it more quickly round its circularpath. However since the end portion 49 is relieved by the surface 52,then the drive plate 34, driven by coil spring 37, drops cleanly pastpin 48 when the latter reaches position D The pin 48 then continues totravel around its circular path 54 from position D until it contacts thedrive plate 34 at B when the cycle repeats. It will be appreciated thateven if the extent of winding or unwinding of the spring is notsuccessively the same from position B to position D of the pin 48 thespring can restore itself to normal whilst the drive plate is movingfrom position E to position A.

The manner in which the sleeve 28 can be moved relative to the pistonrod 26 has been described above. In FIG. 2 the sleeve is shown in itslowermost position but the sleeve may be lifted relative to the pistonrod 26 and thus will also lift the drive plate 34 relative to the pistonrod. The effect of this is to raise the lowermost position of driveplate 34, that is, its position when the piston 22 abuts the valve 17.Thus in FIG. 3 the position A is raised of the drive plate 34 somewhat.In this case it will be seen that the pin 48 will not contact the driveplate 34 until further around its circular path 54 and thus the driveplate 34 will not be moved such a great distance and the stroke of thepump will be correspondingly reduced.

Whilst the above arrangement operates quite satisfactorily it will beappreciated that the motor is idling for approximately half the timefrom the position D of the pin 48 to the position B. A second pin maytherefore be provided on the transverse block 47 diametrically oppositethe first pin 48 and disposed similarly to the first pin. In this casewhen the first pin has passed position D the second pin will beapproaching position D and will immediately start to raise the driveplate 34 and thence the pistons. In this case the speed of the motor canbe halved so that a smaller capacity motor can be used. This provides afurther saving in cost.

It will be appreciated that since the pin 48 is acting on one side ofthe drive plate 34 there is a couple on the piston assembly and partlyfor this reason two pistons 22 and 27 are spaced apart to counteractthis couple. At the same time the piston 27 can act as a backup pistonthe piston 22.

The pump shown in FIGS. 5 and 6 is similar to that shown in FIGS. 1 and2 except in certain respects to be described below.

Referring to FIGS. 5 and 6, a pump comprises a cylinder barrel 60 havingan open upper end and a lower end closed by a plug member 61, the plugmember 61 being mounted in an enlarged end portion 62 of the cylinderbarrel 60. This end portion 62 includes a lower chamber 63 incommunication with the remainder of the cylinder and a fluid inlet 64.The latter is closed by a non-return valve in the form of a ball 65.Lower chamber 63 is divided into an inner chamber 66 and an outerchamber 67 by an filter 68 of annular crosssection.

The cylinder barrel 60 is rigidly connected to lid 69 by means of twostays 70. The stays 70 pass from lid 69 downwardly parallel to the axisof the cylinder barrel 60, thw lower parts of the stays 70 being bentinwardly towards the cylinder barrel 60 and inserted in holes in endportion 62. The stays 70 extend through these holes into the outerchamber 67. The lower end of the stays 70 are sealingly engaged with theend portion 62 to prevent fluid leakage from the lower chamber 63. Oneof the stays, 71, is hollow and of tubular form, the upper end of thetubular stay being mounted in lid 69 so as to communicate via a passage72 with a fluid outlet 73. The other stay 74, is solid.

Cylinder barrel 60 provides a pumping chamber in which is slidable ahollow piston 75 which extends upwardly out of the cylinder barrel andis connected at its upper end to drive plate 76. A piston follower 77 isslidable within piston 75 against a coil spring 78. Coil spring 78extends from the bottom of hollowed out portion 79 of piston 75. Asecond coil spring extending from a flange 80 provided on pistonfollower 77, surrounds narrow portion 81 of piston follower 77. Aboveflange 80 the piston floower 77 has a diameter slightly wider than thenarrow portion 80. As shown piston follower 77 is in its uppermostposition relative to piston 75, flange 80 abutting against shoulder 82of drive plate 76. Further upward movement of piston follower 77 causesdrive plate 76 and piston 75 to move upwardly. The upper end of pistonfollower 77 is rigidly attached to the bottom of sleeve 83 which in turncarries a lever 85 which is pivoted about a point 86 disposed above theupper end of hollow stay 71. Lever 85 may be used for priming the pump.

Referring to FIGS. 1, 2, and 6, the drive means which lifts piston 75against the bias of coil spring 87, differ from that described inconnexion with FIGS. 1 and 2 in that gear wheel 88 carried by the driveoutput shaft is provided between further gear wheel 89 and transverseblock 90. However, functions and relative dispositions of transverseblock 90, pin 91 and drive plate 76 are identical with the abovedescribed embodimerit.

The operation of the piston by the drive means is as described inconnexion with the embodiment shown in FIGS. 1 and 2. However, when thepiston is operated by means of lever 85, it is possible that the pistonfollower 77 will be caused to move downwardly at a greater speed thanthat provided when the piston is being urged by coil spring 87. However,coil spring 78 is chosen such that if an excessive force is applied topiston rod 77 then spring 78 will be compressed by relative movement ofpiston follower 77 within hollow piston 75. Piston will then be urgeddownwardly solely by spring 87.

We claim:

1. A drive arrangement for converting rotary motion to linear motioncomprising:

a rotatable member rotatable about an axis;

a co-operating pin mounted on said rotatable member and spaced from saidaxis;

a co-operating cam member mounted on a shaft extending along a linetransverse to said axis and rotatable about its own axis;

said shaft being arranged for movement by the cam member in only onedirection along said line; a resilient coil spring mounted coaxially onsaid shaft for biasing said cam member in an opposite direction alongsaid line; said cam member rotatively mounted on said shaft for movementgenerally transversely of both said line and said axis of the rotatablemember, said coil spring bearing on said shaft so that the movement ofsaid cam member transversely of said line causes said coil spring towind and unwind, said co-operating pin contacting said cam memberdirectly when said rotatable member rotates with said co-operating pindescribing a circular path about said axis of said rotatable member,said cam member moving said shaft longitudinally in said one directionduring travel of said pin on a portion of said circular path anddisengaged from said cam member when said shaft is moved in saidopposite direction by said coil spring during travel of said pin on theremaining portion of said circular path.

2. A piston pump incorporating a drive arrangement according to claim 1,and wherein said shaft is connected to a piston of said pump.

1. A drive arrangement for converting rotary motion to linear motioncomprising: a rotatable member rotatable abOut an axis; a co-operatingpin mounted on said rotatable member and spaced from said axis; aco-operating cam member mounted on a shaft extending along a linetransverse to said axis and rotatable about its own axis; said shaftbeing arranged for movement by the cam member in only one directionalong said line; a resilient coil spring mounted coaxially on said shaftfor biasing said cam member in an opposite direction along said line;said cam member rotatively mounted on said shaft for movement generallytransversely of both said line and said axis of the rotatable member,said coil spring bearing on said shaft so that the movement of said cammember transversely of said line causes said coil spring to wind andunwind, said co-operating pin contacting said cam member directly whensaid rotatable member rotates with said co-operating pin describing acircular path about said axis of said rotatable member, said cam membermoving said shaft longitudinally in said one direction during travel ofsaid pin on a portion of said circular path and disengaged from said cammember when said shaft is moved in said opposite direction by said coilspring during travel of said pin on the remaining portion of saidcircular path.
 2. A piston pump incorporating a drive arrangementaccording to claim 1, and wherein said shaft is connected to a piston ofsaid pump.